The present invention relates to a high-frequency-discharge excited gas laser, and more particularly to a laser of this kind with augmented output capacity.
A high-frequency-discharge excited gas laser has the following advantages:
(i) it is especially suitable to make a CO.sub.2 laser, which employs highly reactive CO.sub.2 gas, since metallic electrodes do not come in contact with the laser gas;
(ii) being of a capacitive ballast type, the laser has high energy efficiency;
(iii) since a transverse electric discharge requiring relatively low voltage can be used, a power source composed of solid state devices will suffice, so that the size of the equipment can be reduced; and
(iv) good electric discharge uniformity is obtainable using this excitation mode, resulting in good output beam characteristics.
For these reasons, the high-frequency-discharge excited gas laser
(i) can be made small,
(ii) performs with high efficiency, and
(iii) produces good output beam characteristics; and moreover makes an excellent CO.sub.2 gas laser for tooling or machining applications such as cutting.
In order to secure stable electric discharge, the high-frequency-discharge excited gas laser is constructed such that the voltage drop that occurs between the surfaces of the dielectric layer is of the same magnitude as the discharge sustaining voltage. Here, employed as the ballast for obtaining uniform electric discharge is a capacitive ballast which consumes less electric power than a resistor ballast does. Electrodes 10, 10 of a conventional high-frequency-discharge excited CO.sub.2 laser each comprise, as shown in FIGS. 1 and 2, an iron tube 11 and a glass lining layer 12 of thickness 0.8-1.2 mm coated on the iron tube 11. Laser gas is excited as a high frequency voltage from a high frequency power source 13 is applied to the iron tubes 11, 11 of the respective electrodes 10, 10. Since the discharge sustaining voltage for the laser is 5-10 kV, about the same voltage is applied to the lining layer 12. Therefore, the layer 12 must be able to withstand the voltage of 5 kV at the lowest.
To make a strong coat on the iron tube 11, the material of the lining layer 12 ought to be of a kind which sticks itself firmly on the iron tube 11 and ought to have a thermal expansion coefficient equal to that of the iron tube 11, lest the layer 12 should peel off as the iron tube 11 expands with heat. Therefore, it was not sufficient to select a material for the lining layer 12 only from the viewpoint of electrical properties. Also, since the conventional layer is formed through a coating process, pinholes are unavoidable. It undergoes dielectric breakdown as the current applied is increased. If such dielectric breakdown occurs or pinholes exist, the current concentrates there, so that it is difficult to increase the current; that is, the input electric power cannot be raised beyond a certain level, e.g., 1 kW. Therefore, with a conventional laser of this kind, it is difficult to increase the input electric power by increasing the current density, and for this reason it was necessary to enlarge the electric discharge region. As a result, the distance between the electrodes need be greater than 40 mm, wherefore it was difficult to obtain a good TEM.sub.00 mode. Another reason for the difficulty in obtaining a good beam mode is the fact that this kind of electrode structure is adopted for an orthogonal type laser.